Electrical methods of geophysical prospecting have been known for a considerable period of time. Leaving aside self-potential methods, the systems ordinarily employ either an alternating current or direct current power source to apply electric current to the ground between two spaced electrodes. The resultant potential drop is measured either between these electrodes or between other electrodes spaced from them.
Generally speaking, when a solid conductor such as a metal stake or the like is applied to the earth, the chemical make-up of the earth at the particular point and the concentration and kind of ions in the water in pores in the earth cause varying potentials to be generated at the electrode contacts, and also affect the resistance between the conductor and the earth. These two phenomena are usually called polarization. It was found years ago that if the earth were energized with alternating current instead of direct current, the amount of polarization at the contact of electrodes with the ground was very much reduced. However, if the spacing between the electrodes was greater than a few feet, the phenomenon known as "skin effect" was present, that is, the inductive effects of the alternating current flowing to the earth were such that there was considerable modification of the paths of current flow, differing widely from that found when direct current was used. In general, skin effect caused the major path or average path of current flow through the earth to be much more limited to the direct line path between the power electrodes than was the case when direct currents were employed.
As various investigators discovered that it was possible to cope with the polarization problem if one wished to obtain the deep penetration with direct current electrode arrangements by allowing polarization to occur at the power electrodes, and by employing what are termed "porous pot electrodes" at the contact points between which the potential was to be measured. This arrangement has been described well in a number of applied geophysics textbooks, for example in that of J. J. Jakosky, "Exploration Geophysics," published by Times-Mirror Press, Los Angeles, Calif. (1940). Basically one employed a permeable ceramic pot, usually in the shape of a right cylinder with an open top. The inside of the pot held a saturated solution of the salt of some metal, and an electrode of that particular metal was immersed in the solution, giving as much surface contact as possible. Under steady state conditions, these electrodes could be planted on the earth's surface with relatively negligible generated polarization voltage between them. Of course, they could not be employed for ordinary electric well logging, since the hydrostatic pressure of the well fluids surrounding such an electrode would force the well liquids into the pot. In well logging, accordingly, ordinary procedure is to use relatively close spacing between power and potential electrodes, metal electrodes, and alternating potential, the frequency of which usually was above that of the 50-60 Hz power range, but ordinarily only a few hundred hertz, say 400 Hz.
Aside form the nonpolarizing porous electrodes described above, I have been unable to find in a careful search of the literature (including patents dealing with electric surface prospecting and well logging) any variety of nonpolarizing electrode system.